I have encountered similar issues with my various GNU/Linux OS's not showing in the BIOS on the main screen where boot order is just a case of sliding up to the top. Can you see the drive if you go to the Boot Order page? That is what I have had to do after looking at my Q4OS drive which I haven't done in a while.
Just to add, I had managed to get Q4OS to dual-boot on my youngest's PC prior to it having a TPM 2.0 chip installed for Windows 11. Running ZorinOS in live mode and using the Boot Repair utility indicated it needed the Debian x64.efi installing, which I don't have a clue how to do, so suspect it will be a similar EFi thing with your issue with Zorin. I think what happens is Windows (as usual) thinks it knows best and overwrites the EFI file in BIOS - await for others with more experience than me!
Can someone check this suggestion out?:
" Windows 10 has deleted or overwritten the Linux EFI boot entry, you can restore the ability to boot into Linux by reconstructing the GRUB bootloader or using a boot manager like rEFInd. First, ensure the Ubuntu installation is intact, as the recovery process will fail if critical files are missing. Boot from a live USB or CD-R version of rEFInd, disable Secure Boot if necessary, and use rEFInd to access the Ubuntu boot option. If a separate /boot partition is used, you may need to manually add the root filesystem parameter (e.g., root=/dev/sda6 ) using the F2 or Insert key to open a text editor.
Once booted into Ubuntu, reinstall GRUB using the command sudo grub-install at a terminal prompt.
Alternatively, install rEFInd directly to the hard disk via its Debian package or PPA. If you choose to reinstall GRUB, the process will restore the missing grubx64.efi file and related entries on the EFI System Partition (ESP), effectively repairing the boot list.
If the EFI partition itself was corrupted or deleted, you may need to recreate it. Use a Windows 10 installation USB or DVD to boot in UEFI mode, open a command prompt with Shift+F10, and use diskpart to select the appropriate disk and partition, assign a temporary drive letter (e.g., G: ), and run bcdboot C:\Windows /s G: /f ALL to rebuild the Windows boot files.
Afterward, manually add a Windows boot entry to the Linux bootloader configuration by editing /boot/efi/loader/entries/windows.conf and adding the appropriate efi path and title . You can also use tools like EasyUEFI to manually create a new EFI boot entry pointing to \\EFI\\ubuntu\\shimx64.efi .
For a more direct approach, if the original Linux EFI files are still accessible (e.g., from a backup or a mounted ISO), copy them back to the ESP and ensure the boot order is correct using efibootmgr in Linux.
If the system uses a dual-boot setup, ensure GRUB is installed to the correct EFI partition, as Windows may have overwritten the boot order or overwritten GRUB files."